The Home Office could be split into two separate departments "within months", government sources have told the BBC.
Gordon Brown, left, with John Reid and Lord Falconer
Home Secretary John Reid has suggested a split to create one justice ministry and one focusing on public protection.
Constitutional Affairs Secretary Lord Falconer said "the time might well have come" for a split, and former home secretary Jack Straw backed the idea.
But William Hague, for the Tories, called the plan "a pretty serious admission of failure" by John Reid.
And another former Labour home secretary, David Blunkett, told ITV's Sunday Edition that if the split happened there would only be two powerful figures in Cabinet - the prime minister and the chancellor - and that would not be good for balanced government.
The plans sketched out by Mr Reid are set be to put to the Cabinet for discussion at some time in the next few weeks.
Mr Reid famously said it was not fit for purpose when he gave evidence to MPs on the state of Home Office shortly after taking the job in May last year.
Since then he has been reviewing the way it works and its structure as he seeks to end the long sequence of problems the department has faced on issues ranging from immigration to crimes abroad not being recorded on the national crime database.
Under Mr Reid's recommendations, the security department would be responsible for anti-terrorism policy, immigration and the security services.
The Ministry of Justice would have control of probation, prisons and stopping reoffending.
Writing in the Sunday Telegraph, Mr Reid said there would be "no sacred cows when it comes to protecting security and administering justice".
"Whilst in the short term my focus will be on putting right that which needs the most urgent attention - including the way we deal with the transfer of criminal records information and prison pressures - in the long term even more radical change may be unavoidable," he said.
Mr Reid has discussed the plans with senior government figures - although it is not known whether that includes Chancellor Gordon Brown, who is seen as the man most likely to replace Tony Blair as prime minister when he steps down this year.
Lord Falconer, whose department would become a Ministry of Justice, told BBC One's Sunday AM such a split had been "considered a number of times before".
He said: "I think it may well be that that split's time has come as we face, for example, much greater waves of immigration across the world, much greater threats of terrorism."
Jack Straw, who was home secretary from 1997 to 2001, told the BBC he had not backed such a plan then, but terrorism had since become an "overwhelming" issue, and he now thought it was a good idea.
He paid tribute to Mr Reid's willingness to propose a plan despite the fact it would lead him to have a "slightly smaller empire".
Shadow home secretary David Davis said there was an argument for an extra Cabinet minister within the Home Office with specific responsibility for homeland security, but said a split could create "a whole new set of problems".
And shadow foreign secretary William Hague told Sky News' Sunday Live programme "many of the huge problems we have seen in the Home Office in the last year or so have been problems of co-ordination between the different departments".
Mr Hague also warned against a "massive upheaval which is often the excuse for doing nothing in the meantime".
Lib Dem leader Sir Menzies Campbell questioned the fact the plan was announced in a newspaper article but told Sunday AM such a split had been Lib Dem policy.
He said: "We need a Ministry of Justice. There's no doubt whatsoever that by doing that we would allow the remainder of the Home Office, under whatever name it has, to concentrate on these issues of security. "
The recommendations are the result of a review Mr Reid set in motion last May when he moved into the Home Office.
He took over as home secretary after Charles Clarke was sacked in a row over foreign criminals released from prison without being considered for deportation.
But since then Mr Reid's department has continued hitting the headlines.
Earlier this month it emerged that more than 27,000 case files on Britons who had committed crimes abroad, including rape and murder, had not been entered on the police computer.
It also emerged that a third terror suspect on a control order had absconded.
And before that there was a row when it emerged the head of the Prison Service did not know how many inmates were on the run from open jails in England.